More heuristics.
 [rsc] --rw-rw-r-- M 191333 presotto sys 18523 Sep 22 08:38 sys/src/cmd/cb/cb.c
	/n/sourcesdump/2005/0922/plan9/sys/src/cmd/cb/cb.c:466,471 - 
	/n/sourcesdump/2005/0923/plan9/sys/src/cmd/cb/cb.c:466,476
	  			gotop(c);
	  			continue;
	  		case ':':
	+ 			if ((cc = getch()) == ':') {
	+ 				putch(c,NO);
	+ 				putch(cc,NO);
	+ 				continue;
	+ 			}
	  			if (question == 1){
	  				question = 0;
	  				gotop(c);
	/n/sourcesdump/2005/0922/plan9/sys/src/cmd/cb/cb.c:796,802 - 
	/n/sourcesdump/2005/0923/plan9/sys/src/cmd/cb/cb.c:801,807
	  			lbegin = 0;
	  			if (split == 1){
	  				split = 0;
	- 				if (clev->tabs > 0)Bprint(output, "    ");
	+ 				if (clev->tabs > 0)Bprint(output, "\t");
	  			}
	  		}
	  		*p = '\0';
 [sys] --rwxrwxr-x M 191333 presotto sys 77589 Sep 22 23:10 386/bin/cb
	/sys/src/cmd/cb/cb.c:error
	/sys/src/cmd/cb/cb.c:outs
	/sys/src/cmd/cb/cb.c:puttmp
	/sys/src/cmd/cb/cb.c:work